In a typical solar power plant, solar power are collected by a plurality of photovoltaic (PV) devices or panels transforming the solar power into DC (direct current) electric power, which power is subsequently converted into AC (alternating current) electric power of a power transmission system or grid.
The power is collected at a low voltage by the PV panels, converted into a higher voltage and fed to the transmission system. To provide the conversion a complex system is used incorporating many devices and to maximize efficiency different collecting and conversion systems have been used.
US 2012/0274139 (E1) describes a distributed PV power plant including a plurality of distributed DC/DC converters (22 in E1), each being connected to a plurality of strings of PV panels. The switching of the DC/DC converters is coordinated, and their power are supplied to a common DC bus for further conversion by means of a DC/AC converter into AC power (see FIG. 1-4, claim 1 of E1). By coordinating the switching of the local DC/DC converters a higher efficiency can be provided (see §0032, §0036 in E1).
Another method and system for enhancing efficiency is disclosed in US2011/0160930 (E2). Document E2 describes a solar power plant comprising photovoltaic panels (PV panels) (20 in FIG. 3 of E2), local power converters (22 in E2) and a central power converter (24 in E2). So called maximum power point tracking (MPPT) is provided for each power source, i.e. for each PV panel, by means of the local power converters (22, see §0006, §0021, see also FIG. 4 and FIG. 5 in E2). The central converter (24) also includes MPP tracking (see §0025, claim 1 in E2), and the two methods of MPP tracking are coordinated (see §0061, FIGS. 16-18) in E2. Such a system has benefits during for example shading, but the provision of one dedicated local converter for each panel adds costs to the overall system, especially for larger systems.